1. Field of the Invention
The present invention relates generally to a motorcycle and a body structure therefor. More particularly, the invention relates to a body structure for a motorcycle of the type which includes a body frame having an engine mounted thereon, a front leading arm for supporting a front wheel, the front leading arm being vertically swingably joined to the body frame, and a rear trailing arm for supporting a rear wheel, the rear trailing arm being vertically swingably joined to the body frame.
2. Description of Relevant Art
There has been proposed a motorcycle with a body structure including a body frame having a power unit disposed substantially in a central portion thereof, a swingable front arm extending forwardly of the power unit for supporting a front wheel, and a rear swingable arm extending rearwardly of the power unit for supporting a rear wheel. Such a structure is disclosed, for example, in Japanese Laid-Open Application No. JP-A-53-142739 laid open Dec. 12, 1978 and Japanese Laid-Open Application No. JP-A-54-122538 laid open Sept. 22, 1979.
In the structures disclosed in the aforesaid laid-open applications, the arm supporting the front wheel is a leading type front arm extending forwardly from a body frame having an engine mounted thereon, substantially linearly in the side view.
For example, in the aforesaid Japanese Application No JP-A-54-122538, as shown in FIG. 10 of the accompanying drawings, there are employed upper and lower front leading arms 91, 93 which are vertically swingably pivoted at their rear ends 91a, 93a on a body frame side member 90 fastened to an engine (not shown), respectively, the upper and lower front arms 91, 93 both extending forwardly of the member 90, substantially linearly in the side view and substantially parallel with each other. The front ends of the arms 91, 93 have a steering plate 95 operatively interposed therebetween for supporting in a cantilever manner an axle 97 of a front wheel 96. In FIG. 10, the left corresponds to the front of the member 90.
In a body structure for motorcycles having a front suspension with such a front leading arm, there is generally employed a cushion means for the suspension. In the structure disclosed in the aforesaid Japanese Application No. JP-A-54-122538, a single hydraulic damper (not shown) of a telescopic type is employed as such a cushion means, which damper is pivotably connected at its lower end to the substantially longitudinally intermediate part of the lower front arm 93 and at its upper end to a portion of the body frame side member 90 slightly above the upper front arm 91.
The steering plate 95 is adapted to be operable for steering the front wheel 96 with a steering mechanism (not shown) comprising a handlebar, a steering shaft, a knuckle arm, and a tie rod.
Further, in the structure disclosed in the aforesaid Japanese Application No. JP-A-54-122538, although not shown in the accompanying drawings, the aforesaid rear trailing arm, which comprises a swing arm vertically swingably pivoted at its front end on a body frame side member, constitutes a rear suspension having as a cushion means thereof a single hydraulic damper of a telescopic type. The damper is pivotably connected at its upper end to a body frame and at its lower end to a linkage interposed between the body frame and the rear trailing arm, the linkage comprising a small swingable arm and a connecting rod.
In the motorcycle proposed in the aforesaid Japanese Application No JP-A-53-142739, although the entire structure thereof is substantially the same as that disclosed in Japanese Application No. JP-A-54-122538, there are employed front and rear dampers both disposed higher than those of the latter case, thus going against the current trend of lowering the center of gravity.
In such conventional motorcycles, particularly in a motorcycle according to the aforesaid Japanese Application No. JP-A-54-122538, a front wheel can be steered independently of a front suspension, i.e., without requiring an accompanying movement such as of a damper and a leading arm, so that the steering load of the front wheel is remarkably decreased, thereby providing a favorably light steering of the front wheel in comparison with that of a well-known steering head type motorcycle in which a front fork and a pair of dampers constitute a front suspension.
However, as shown in FIG. 11 of the accompanying drawings, which is a bottom view of each front leading arm of FIG. 10, the front leading arm 93 (91) has a longitudinally intermediate portion 94 (92) thereof curved leftwardly of the motorcycle to provide a necessary steering angle .alpha..sub.0 for the front wheel 96, which curved portion 94 (92) is therefore required to have an offset distance .delta..sub.0 with respect to a longitudinal center line N.sub.0 of the motorcycle, so that the motorcycle has an increased width. In this respect, decreasing the offset distance .delta..sub.0 will result in failure to attain the steering angle .alpha..sub.0.
Moreover, in a motorcycle of the type in question, although an engine contributes to some extent to the attainment of an increased rigidity of a body frame, there is a desideratum, in view of the recent trend of mounting a heavy V-type engine with at least a pair of combustion cylinders arranged at the front and rear to attain a high-power outout, for a body structure able to provide a sufficient rigidity and strength of the body frame, while providing a sufficiently lightweight body frame to offset the weight of the V-type engine.
Further, in the known body structure of the type in question, the body frame with an engine mounted thereon has, at its front and rear ends, front and rear dampers extending forwardly and rearwardly therefrom, respectively, thus failing to contribute to a compact design of a wheel base or to lowering of the center of gravity of the motorcycle.
The present invention effectively overcomes the disadvantages and shortcomings attendant a conventional body structure for motorcycles as described above, while at the same time fulfilling the aforesaid desideratum.